1. Field of the Invention
This invention relates to an unburnt refractory mass in the form of granules, bricks or the like for use in vessels employed for metallurgical refining. More especially, this invention relates to an unburnt refractory mass consisting essentially of chromium ore and a carbon-containing binder and optionally including a proportion of sintered magnesia.
2. Discussion of the Prior Art
Refractory masses or bricks have long been known for use in metallurgical vessels. It has also been known to employ refractory masses or bricks in the burnt state made from chromium ore. It is known that such refractory masses or bricks have a desirable resistance to basic and acid slags. Unfortunately such burnt refractory masses or bricks have unsatisfactory physical properties with respect to changes in temperature and stability. It is also known that metallurgical vessels formed from burnt chromium-containing refractory masses are subject to bursting. A survey of typical bricks formed from chromium-containing masses is given in LUEGER "Lexikon der Huttentechnik" (1973), page 115.
Unburnt refractory masses or bricks containing chromium ore components have also been described in German Pat. No. 667 691, German Auslegeschrift No. 1 014 913 and German Auslegeschrift No. 1 646 837. German Pat. No. 667 691 describes a chromium ore-containing refractory mass containing less than 3% silica and containing inorganic binding materials such as colloidal silica or volatilizable materials such as tar or drying oils. Sulfite liquor is also described therein as a suitable binder.
German Auslegeschrift No. 1 014 913 describes a non-acid refractory mass or brick, particularly an unburnt refractory brick derived from a mixture of chromium ore and burnt magnesia. Sulfuric acid, acidic sodium sulfate, magnesium sulfate, magnesium chloride, sulfur liquor or other organic binders are described as useful binders therefore. As the slag resistance, stability, cold crushing strength and resistance to changes in temperature of known refractory masses containing chromium ore components is unsatisfactory it is proposed in German Auslegeschrift No. 1 646 837 to burn a mixture of chromium ore and magnesite to produce a simultaneous sinter as an initial product and to bring up this simultaneous sinter for the production of unburnt bricks. In this previously known process it was considered essential that the simultaneous sinter already have the properties of the burning at elevated temperature, i.e., the direct bond between the chromium oxide containing materials and the magnesia. To produce the bricks, the sintered material in granular form was mixed in a known manner with tar and/or pitch and then formed into bricks. These bricks should have produced an extended strength in relationship to other chromium based bricks in the open hearth furnace. Unfortunately the production of a simultaneous sinter requires a subsequently performed burning process.
It became desirable, therefore, to provide a refractory mass resistant to both acid and basic sludges having improved physical properties with respect to resistance upon being subjected to changes in temperature. It became especially desirable to provide such a refractory mass in granular or in brick form which was unburnt and did not require a superposed burning process. Still moreover, it became desirable to provide a suitable refractory mass for use in metallurgical refining vessels whereby the components of such refractory mass would not interfere with the metallurgical refining process or in the purity of the components derived therefrom. It has become desirable especially to provide a refractory mass or brick for use in the walls of ladles employed in ladle degassing, desulfurization, melt alloying and similar refining steps. Such has become desirable because of the refining practice whereby steel at higher temperatures is tapped into a ladle thereby subjecting the ladle to significant temperature change. It has been discovered that the previously employed lining material for such vessels based upon alumina, silica or both no longer satisfies the requirements. Hence, it has become desirable to provide a suitable replacement for the linings of ladles heretofore lined with basic products especially alumina or silica alumina containing over 60% by weight Al.sub.2 O.sub.3.